Communities

What is a community?

Communities are populations of organisms that interact
with each other. As with each level of organization in the living
world, certain
phenomena in a community act to shape and sustain it.
The interactions among different populations are what hold a
community together. Some
interactions involve the provision of habitat. A good example
is a tree that houses birds, insects, and other creatures. Other
vital interactions involve reproduction, such as plants that
are pollinated
by insects. Symbiotic interactions, such as the relationship
between algae and fungi in lichens, are also important.

The sea life that
gathers around a
wreck is an example of a community

Without
a doubt, the most important interactions in a community involve
energy flow — the transfer of energy along food chains
from one organism to the next. Without this flow of energy, individual
organisms cannot survive and the community collapses.

How does
energy flow in a community?

In any community, there are the producers,
consumers, and decomposers. Producers include plants and some
protists, bacteria, and archaea.
These individuals take in energy in an inorganic (i.e., nonliving)
form, such as light, and change it into food, which is an organic
form of energy. This energy is used or stored in the organic
molecules that
compose a producer’s body.

Consumers are organisms that can’t
make their own food. The most familiar consumers to us are animals.
They represent the “typical” consumer
in that they ingest food to obtain energy. Some animal consumers
eat plants, some eat other animals, and some eat a variety of
food sources.
Certain protists, like the amoeba, are also consumers.

A special
group of consumers is the decomposers. Like other consumers,
they can’t
make their own food. They differ from other consumers because
they obtain their energy by decomposing the bodies of
dead things. They secrete digestive chemicals onto their food
and break large molecules into smaller ones that they then absorb.
The
most important
decomposers in most communities are the fungi and the bacteria.
Some protists and archaea are also decomposers.